This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-113654, filed Apr. 21, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to a cathode-ray tube and a method of manufacturing the same and, more specifically, to a cathode-ray tube of divided scanning a phosphor screen with electron beams emitted from a plurality of electron guns and a method for manufacturing the same.
In recent years, various discussions have been made on a high-resolution cathode-ray tube designed for high-definition broadcasting or having a large screen. For providing a cathode-ray tube with a high resolution, the diameter of a spot of an electron beam on the phosphor screen must be minimized. In contrast, the structures of electrodes constituting an electron gun have been improved or the electron gun itself has been remodeled to have a larger aperture or a larger length. However, no fruit has been born yet.
As the cathode-ray tube is made large in size, the distance from the electron gun to the phosphor screen becomes long, and the power of an electronic lens becomes too high. This is the most critical reason why no fruit has been born yet. Consequently, for realizing a high resolution, the distance from the electron gun to the phosphor screen (depth) must be decreased. At this time, if an electron beam is deflected at a wide angle, a difference in magnification between the center of the screen and the periphery thereof increases. This is therefore unacceptable in terms of the high resolution.
According to a conventionally adopted method, a plurality of electron guns and a plurality of deflection yokes are employed in order to divided scan a plurality of regions defined of a single phosphor screen. Images rendered in the regions are joined to produce a large image. For example, Jpn. Pat. Appln. KOKAI Publication Nos. 7-45215 and 2-51831 have disclosed cathode-ray tubes for joining two images to produce a large picture. Moreover, Japanese Unexamined Patent Publications Nods. 61-256552 and 61-256551 have proposed cathode-ray tubes for joining a larger number of images to produce a large picture.
This kind of cathode-ray tube has a vacuum envelope having a panel, a funnel including two corn portions and coupled to the panel, and two necks coupled to the funnel. A deflection unit is mounted on the external surface of each corn portion. An electron gun is arranged in each neck.
In the cathode-ray tube having the above components, electron beams emitted from the electron gun are deflected due to magnetic fields generated by the deflection units. A phosphor screen formed on the inner surface of the panel has two regions corresponding to the electron guns and the two regions are divided scanned by the electron beams. Sub-images rendered on the phosphor screen are joined by controlling signals to be applied to the electron guns and deflection units. Consequently, one large image having neither a break nor overlap is produced over the whole surface of the phosphor screen.
The panel of the cathode-ray tube described above is formed by pressing using a forming mold by the same method as that of manufacturing a conventional cathode-ray tube. More specifically, the forming mold has a bottom and a shell ring provided detachable from the bottom, and a plunger can be inserted into the cavities of the bottom and shell ring.
In forming the panel, a glass gob (high-temperature glass gob) is supplied to the bottom to fix the shell ring and push the plunger into the mold. The panel so formed is cooled and then the shell ring is detached from the bottom, thereby removing a molding product therefrom.
However, upon manufacturing the cathode-ray tube described above, the funnels may be broken in the cooling step after pressing, due to the difference between thermal expansion coefficient of materials of the bottom and the glass. Thus, the funnels of the cathode-ray tube cannot be formed by pressing using the same method as that of forming a conventional cathode-ray tube.
The present invention has been developed in consideration of the above situation and its object is to provide a cathode-ray tube wherein a phosphor screen is divided scanned with electron beams emitted from a plurality of electron guns, and wherein funnels can be formed easily and inexpensively making use of a conventional pressing process, and a method for manufacturing the same cathode-ray tube.
To attain the above object, a cathode-ray tube according to the present invention comprises:
a vacuum envelope including a glass panel having a phosphor screen on an inner surface thereof, a funnel section having a plurality of cone sections and joined to the glass panel, and a plurality of necks extending from the cone sections respectively;
a plurality of deflection devices mounted outside the cone sections; and
a plurality of electron guns arranged in the necks, respectively, for divided scanning a plurality of scanning regions of the phosphor screen with electron beams,
wherein the funnel section includes a plurality of funnels each formed by cutting at least one side portion of a base funnel which is so formed as to have one cone section, and the funnels have respective sections joined to each other.
A method for manufacturing a cathode-ray tube according to the present invention, comprises a vacuum envelope including a glass panel having a phosphor screen on an inner surface thereof, a funnel section having a plurality of cone sections and joined to the glass panel, and a plurality of necks extending from the cone sections respectively; a plurality of deflection devices mounted outside the cone sections; and a plurality of electron guns provided in the necks, respectively, for divided scanning a plurality of scanning regions of the phosphor screen with electron beams, the method comprising the steps of:
preparing a plurality of base funnels;
cutting at least one side portion of each of the base funnels to form a plurality of funnels; and
joining sections of the funnels to each other and joining the funnels to the glass panel to form the vacuum envelope.
According to the cathode-ray tube so constituted and the method for manufacturing the same, a plurality of glass funnels are each formed by cutting at least one side portion of a base funnel formed by pressing and the funnels are joined together into a funnel section. Therefore, the cathode-ray tube can be manufactured easily and inexpensively and the method for manufacturing the same can be provided.
In other words, each of the glass funnels has a cone section and is formed by cutting part of a funnel having the same shape as that of a funnel of a conventional cathode-ray tube. The glass funnels can thus be formed easily by pressing by the same method and using the same forming mold as in a conventional cathode-ray tube. The existent glass cutting technique can be applied to cutting of the funnels, and the conventional sealing process can be used for joining the funnels together. Consequently, there can be provided with a cathode-ray tube capable of being manufactured easily and inexpensively making use of the conventional pressing process, and a method for manufacturing the same cathode-ray tube.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.